1. Field of the Invention
The present invention relates to an organic photoelectric conversion material having a specific chemical structure and a high-performance organic thin-film photoelectric conversion element obtained using the photoelectric conversion material.
2. Description of the Related Art
Now, in a ubiquitous information society, information terminals which can be used any time anywhere are requested. There is therefore a demand for the development of flexible, light-weight, and inexpensive electronic devices, but conventional electronic devices using an inorganic semiconductor material such as silicon cannot sufficiently satisfy such a demand. Recently, much study has been made on electronic devices using an organic semiconductor material capable of meeting the demand (Chemical Reviews, 107, 1296-1323(2007) and Organic Field-Effect Transistors (published in 2007 by CRC press), pp 159-228).
Organic thin-film photoelectric conversion elements are available by forming an organic semiconductor material into a thin film and using the thin film as a photoelectric conversion material. The organic thin-film photoelectric conversion element can take out, as energy, charges (carriers) generated by light so that it can be utilized as a solar cell (organic thin-film solar cell) (Chemical Reviews, 107, 1324-1338(2007)) or can take them out as an electric signal so that it can be utilized as an optical sensor (solid-state pickup device) (Japanese Patent Laid-Open No. 2003-234460, Japanese Patent Laid-Open No. 2003-332551 and Japanese Patent Laid-Open No. 2005-268609).
Organic semiconductor materials are used advantageously as a photoelectric conversion material because use of them enables production of elements of a large area at a low cost in accordance with the process of application and also enables tuning of characteristics (for example, photoelectric conversion wavelength) of the elements by chemically modifying a photoelectric conversion material. Only limited substances such as phthalocyanines, fullerene derivatives, conductive polymers, and perylenetetracarboxylic acid derivatives offer a high performance as an organic photoelectric conversion material. They however are not easily imparted with solubility or cannot be chemically modified freely and thus, they cannot make full use of the advantage of the organic semiconductor materials. There is therefore a demand for the development of photoelectric conversion materials which can be formed into a film by the process of application, provide great possibility of chemical modification, and permit production of an organic thin-film photoelectric conversion element having a high performance.
Examples of the organic thin-film photoelectric conversion element exhibiting the best characteristics include elements having, as a photoelectric conversion film, a blend film of P3HT (poly(3-hexylthiophene)) and PCBM ([6,6]-Phenyl-C61-butyric acid methyl ester). This element shows a high photoelectric conversion performance, but is inferior in the performance to conventional silicon solar cells. There is therefore a demand for the development of elements exhibiting a higher photoelectric conversion performance (Chemical Reviews, 107, 1324-1338(2007)). Photoelectric conversion materials for organic photoelectric conversion elements having a molecular weight exceeding 800 are described in J. Phys. Chem. C, 111, 8661(2007), but these photoelectric conversion materials is low on photoelectric conversion performance.